Laminae construction for dynamoelectric machines



Patented Jan. 12, 1937 UNITED STATES PATENT OFFICE LAMINAE CONSTRUCTION FOR DYNAMO- ELECTRIC MACHINES poration of Delaware Application March 28, 1935, Serial No. 13,386

1 Claim.

My invention relates to a form of laminae for use in dynamoelectric machines which are to be provided with cast conductors, its object being to avoid certain defects in machines of this kind as heretofore made.

In the accompanying drawing Figure l is a cross-sectional view of a cast squirrel cage rotor of the kind now commonly used and in which the conductor slots are either of the semi-closed type, as illustrated in Figure 2, or of the closed type, as illustrated in Figure 3. Figure 4 illustrates improved laminae construction in accordance with my invention.

Under the present practice of manufacturing cast squirrel cage rotors, the casting material l; (usually aluminum alloy or zinc alloy), whilel in its molten state, flows between the adacent surfaces of the assembled laminae 2 to a sufficient distance, when slots of the standard types are employed, to reach the outer surface of the rotor or sufficiently near said surface, (as indi cated by stippled portions of Figures 2 and 3) that when the rotor is ground or turned in the completion of its manufacture, to obtain the correct and uniform air gap between it and the stator, the tool comes into Contact with the cast conductor material and so distributes it over the rotor as to electrically connect the individual laminae punchings and thereby cause, in the operation of the machine, a heavy eddy current loss on the surface of the rotor which manifests itself in excessive heating and decreased eiciency.

To avoid the above difficulty I provide the 3 laminae punchings with conductor receiving openings formed to produce a machine of the closed slot type, but locate the outer limits of said openings further away from the periphery of the laminae than in accordance with prior practice, these outer limits being radially displaced from the periphery to a sufficienti extent that the outer limit of the penetration of the molten conductor material between adjacent laminae will be sufciently below the periphery of the rotor that during the subsequent finishing operation the nishing tools do not come into contact with it.

The laminae punchings are provided with recesses 3 in their periphery adjacent the outer limits of the conductor receiving openings, whereby the magnetic bridge 4 forming the top of the conductor slots of the rotor, is reduced in radial thickness to as small proportions as mechanically feasible from the standpoint of avoiding deformation of the bridge elements from original shape when the rotor punchings 4are being assembled. I found that suitable proportions are to make the peripheral recesses from .03 to .06 inch deep, and the bridge elements from .01 to .02 inch thick in radial direction.

In applying the molten conductor material to an' assembly of laminae of the structure described, some of the material may pass between. the elements of the bridge and into the bottom of the slots formed by the peripheral recesses, but this material will remain below the finish line of the subsequent grinding or turning operation and since, in the operation of the motor the magnetic eld intensity is relatively low at the bottom of the slots formed. by the; recesses in the laminae, the eddy current losses which may occur due to the smallamount of conductor material which has seeped through the magnetic bridges are very small.

While displacing the conductors further from the periphery of the rotor than in prior machines slightly reduces overload capacity, this is a much less serious disadvantage than those; due to the conductive interconnection of the laminae by the distribution of the casting material over the surface of the rotor under the present methods of manufacture herein described.

I-Iaving fully described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

A laminae assembly for use in forming the rotor or stator element of a dynamoelectric machine, which comprises a plurality of laminae clamped together and having aligned closed slots to receive molten conductive material, the outer ends of said slots being sufficiently displaced from the surface of the assembly that the molten conductive material does not flow between the laminae to said surface, and the laminae being provided recesses in their outer edges and adjacent the outer ends of the slots, the depth of said recesses being such that the radial thickness of the magnetic bridges closing the outer ends of the slots is substantially less than the radial displacement of the ends of the slots from the surface of the assembly.

GEORGE A. GRIFFIN. 

